I read with interest the clinical review by Nyirenda (1) and
colleagues and would like to comment on spurious causes of hyperkalaemia.
When we audited the management of severe hyperkalaemia, defined as a
serum potassium of 7.0 mmol/L or above, we found pseudohyperkalaemia to be
the cause in 25% of the patients studied. We and others (2) have found
that an unexplained serum hyperkalaemia is commonly due to sample
contamination by the anticoagulant potassium ethylene diamine tetra-acetic
acid (K-EDTA) found in sample tubes for haematological blood cell counts.
K-EDTA may be carried over during a difficult sampling procedure from the
haematology tube to the biochemistry blood tube. Not only will this result
in factitiously raised serum potassium, but also a reduced serum calcium,
magnesium and alkaline phosphatase activity. We now routinely test for low
calcium when we find a severe hyperkalaemia to identify EDTA
contamination, and others (3) have found that direct measurement of EDTA
is a better way of doing this. This latter study concluded that gross K-
EDTA contamination is obvious by marked unexpected hyperkalaemia,
hypocalcaemia, hypomagnesaemia and hypozincaemia but that spurious
hyperkalaemia due to low concentrations of K-EDTA contamination can only
be confidently detected by measurement of serum EDTA.
Nyirenda’s review correctly points out the need to first exclude
spurious causes but then advises an exception in severe cases when
immediate treatment is needed. Severe cases, which they define as
potassium levels above 6.5 mmol/L, may, in our experience, be due to K-
EDTA and hence immediate potassium lowering treatment without excluding
artefacts might cause an acute hypokalaemia in such patients and increase
their risk of cardiac arrhythmia.
1. Nyirenda MJ, Tang JI, Padfield PL, Seckl JR. Hyperkalaemia. BMJ.
2009, 339: b4114
2. Sharratt CL, Gilbert CJ, Cornes MC, Ford C, Gama R. EDTA sample
contamination is common and often undetected, putting patients at
unnecessary risk of harm. Int J Clin Pract. 2009, 63:1259-62.
3. Cornes MP, Ford C, Gama R. Spurious hyperkalaemia due to EDTA
contamination: common and not always easy to identify. Ann Clin Biochem.
2008, 45:601-3.
Rapid Response:
Spurious hyperkalaemia
I read with interest the clinical review by Nyirenda (1) and
colleagues and would like to comment on spurious causes of hyperkalaemia.
When we audited the management of severe hyperkalaemia, defined as a
serum potassium of 7.0 mmol/L or above, we found pseudohyperkalaemia to be
the cause in 25% of the patients studied. We and others (2) have found
that an unexplained serum hyperkalaemia is commonly due to sample
contamination by the anticoagulant potassium ethylene diamine tetra-acetic
acid (K-EDTA) found in sample tubes for haematological blood cell counts.
K-EDTA may be carried over during a difficult sampling procedure from the
haematology tube to the biochemistry blood tube. Not only will this result
in factitiously raised serum potassium, but also a reduced serum calcium,
magnesium and alkaline phosphatase activity. We now routinely test for low
calcium when we find a severe hyperkalaemia to identify EDTA
contamination, and others (3) have found that direct measurement of EDTA
is a better way of doing this. This latter study concluded that gross K-
EDTA contamination is obvious by marked unexpected hyperkalaemia,
hypocalcaemia, hypomagnesaemia and hypozincaemia but that spurious
hyperkalaemia due to low concentrations of K-EDTA contamination can only
be confidently detected by measurement of serum EDTA.
Nyirenda’s review correctly points out the need to first exclude
spurious causes but then advises an exception in severe cases when
immediate treatment is needed. Severe cases, which they define as
potassium levels above 6.5 mmol/L, may, in our experience, be due to K-
EDTA and hence immediate potassium lowering treatment without excluding
artefacts might cause an acute hypokalaemia in such patients and increase
their risk of cardiac arrhythmia.
1. Nyirenda MJ, Tang JI, Padfield PL, Seckl JR. Hyperkalaemia. BMJ.
2009, 339: b4114
2. Sharratt CL, Gilbert CJ, Cornes MC, Ford C, Gama R. EDTA sample
contamination is common and often undetected, putting patients at
unnecessary risk of harm. Int J Clin Pract. 2009, 63:1259-62.
3. Cornes MP, Ford C, Gama R. Spurious hyperkalaemia due to EDTA
contamination: common and not always easy to identify. Ann Clin Biochem.
2008, 45:601-3.
Competing interests:
None declared
Competing interests: No competing interests